1. Field of the Invention
The present invention relates to an electron emitting device, and particularly to an electron emitting device used in an electron generator (or electron-generating apparatus). It is also concerned with a method for driving said electron emitting device or electron generator.
2. Related Background Art
Known as solid-state electron beam generators are apparatus in which an electric field is applied to a junction between dissimilar materials, formed in a semiconductor, to cause electron beams to be radiated outside from the surface of the semiconductor.
For example, Japanese Patent Publication No. 54-30274 discloses an apparatus in which a forward voltage is applied to an np junction formed in a mixed crystal of AlP with GaP to cause electrons to be emitted from the surface of a P-type region. Japanese Patent Laid-Open No. 54-111272 discloses a solid-state electron beam generator in which a reverse voltage is applied to a pn junction at least a part of which has been exposed into an opening provided in an insulating layer on the surface of a semiconductor, and also an accelerating electrode is so provided to the insulating layer as to extend to the edge of the opening. Japanese Patent Laid-Open No. 56-15529 also discloses a semiconductor device in which an accelerating electrode is provided at the edge of an opening provided in an insulating layer on the surface of a semiconductor, and a reverse voltage is applied to a pn junction extending, within the opening, in parallel to the surface of the semiconductor to cause electrons to be emitted outside the semiconductor. These Japanese Patent Laid-Open Nos. 54-111272 and 56-15529 each also disclose an electron beam generator comprising electron-emitting devices integrated on a semiconductor substrate, respectively. Also, Japanese Patent Laid-Open No. 57-38528 discloses an electron-emitting multiple cold cathode in which devices capable of emitting electrons from the surface of a semiconductor by applying a bias voltage to a pn junction in the forward direction are integrated on a semiconductor substrate.
These solid-state electron beam generators have a number of advantages such that they are compact and capable of emitting electrons by use of the voltage applied to the pn junction. Making the most of the advantage that they can be made compact, it can be contemplated to provide an apparatus in which a plurality of electron beams are arranged, but the wiring for driving such an electron beam generator becomes complicated, thereby raising another problem.
On the other hand, D. J. Barteling, J. L. Moll and N. I. Meyer report in Phys. Rev. Vol. 130, Number 3 (1963) 972-985 that in instances in which a reverse voltage is applied to cause electron avalenches to generate electrons, it is also possible to irradiate light on the P-type region to excite electrons, thereby driving the generator. Since, however, the light used to excite electrons is incident from the electron beam emission side, this has imposed a great limitation on the manufacture of apparatus that utilize electron beams.